1. Field of the Invention
This invention relates to a vari-focal camera which has a main lens system and an auxiliary lens system included in the photo-taking lens system thereof and is arranged to be shiftable between at least two different focal lengths by allowing the auxiliary lens system to move onto and out of a photo-taking optical axis in response to the movement of the photo-taking optical system.
2. Description of the Prior Art
With the exception of single-lens reflex cameras, photographic cameras, particularly 35 mm cameras with lens shutters, generally use taking lenses of focal lengths 35-40 mm. It is, however, more apposite to use a lens of a focal length suited to the condition of an object to be photographed. In view of this, there have been proposed various cameras of the type wherein an auxilairy lens system is incorporated in the camera in addition to a main lens system. The auxiliary lens system is arranged to move onto and out of a photo-taking optical axis according as the main lens system is moved in such a way as to permit photographing with a composite optical system consisting of the main and auxiliary lens systems as well as the ordinary photography to be performed solely with the main lens system. The cameras of this type include those disclosed in Japanese Laid-Open Patent Application Nos. Sho 52-76919 and Sho 54-33027.
An example of the prior art cameras of the above-stated type permitting not only standard photography but also tele-photography is arranged as shown in FIG. 1 of the accompanying drawings. Referring to FIG. 1, a main lens system L1 has a lens shutter S. The camera is provided further with an auxiliary lens system L2. A reference symbol F denotes a film surface. FIG. 1(a) shows a standard photographing state and FIG. 1(b) a tele-photographing state. In the tele-photographing state, the main lens system L1 and the lens shutter S shift toward the front of the camera while the auxiliary lens system is positioned in rear of the lens shutter S.
As shown, the main lens system and the lens shutter must be moved to the front of the camera while the auxiliary lens system must be in rear of the lens shutter in order to shift the optical system from one focal length to another. This requires highly complex operating mechanism. Besides, light shielding for the camera obscura becomes difficult. Further, the auxiliary lens system must be retracted from the photo-taking optical axis at the time of the standard photography. The retraction requires a stowing space for the auxiliary lens system within the camera body. The size of the camera thus inevitably increases to hinder reduction in size of the camera.
Further, bellows have heretofore been used as light shielding member for the camera obscura part. Generally, however, the bellows are made of a leather or cloth material. The material can be hardly made to be thin and thus requires a large space for having it incorporated in the camera. The light shielding member not only is thus unsuited for reduction in size but also has insufficient durability for preventing a leak of light through a hole which tends to result from repeated use.
Another problem with the vari-focal camera having such a photo-taking optical system resides in so-called infinity focusing required at the different focal lengths of the photo-taking optical system. More specifically, in the event that infinity focusing has been made with the camera set in the state for the standard photography to be performed solely with the main lens system, infinity focusing must be done again when the main lens system is moved to have the auxiliary lens system used in combination with the main lens system. Whereas, in the vari-focal cameras of the prior art that have been proposed in the past have paid no attention to the necessity of this infinity focusing and provided no adjusting means therefore.